1. Field of the Invention
This invention relates to fabrication processes for forming magnetic bubble domain devices, and in particular to fabrication processes providing multiple layer bubble domain devices using only a single masking step.
2. Description of the Prior Art
In the fabrication of magnetic bubble domain devices, it is frequently necessary to deposit multiple magnetic layers in precise alignment with one another. At the same time, it is often necessary that different materials or combinations thereof be placed in different areas of the same circuit structure. For example, it may be desirable to have a high conductivity electrical layer such as gold located between two layers of magnetic material, where one of the layers is used for moving the bubble domains while the other is used as a bubble domain sensor. Additionally, it may also be desirable to place a layer of magnetoresistive material, such as NiFe, in a sensor area of the circuit in order to detect the presence or absence of a bubble domain thereat.
Most processes for fabricating magnetic bubble domain circuits use a plurality, of masking steps to provide the multiple layer structures. For instance, IBM Technical Disclosure Bulletin Volume 15, No. 6, November 1972, p. 1826 describes an example of the prior art processes. In this process, a plurality of masking steps requiring a plurality of alignments is required.
In contrast with a process involving several masking steps, attempts have been made to provide single masking step processes. One such attempt is described in an article by A. H. Bobeck et al which appears in the IEEE Transactions on Magnetics, Volume MAG-9, No. 3, September 1973, at page 474. In the fabrication process described therein, a shadow mask is used to protect the sensor area of the circuit structure during deposition of conductor lines. However, this process has disadvantages when full wafer processing and small bubble domain sensors are utilized. During such processing, the provision of shadow masks requires some alignment when full wafer processing is utilized and the sensor areas to be defined are very small.
Thus, in the prior art, multiple layers of films in bubble domain devices are conventionally formed by the use of multiple masks and multiple photoresists in order to define the respective areas in which each of the layers is to be deposited. It is also possible to use scanned or "programmed" electron beams for this purpose. However, provision of either of these two methods is difficult since it is difficult to align the masks or electron beams precisely when going from one layer deposition to the next. This problem becomes increasingly acute as the sizes of individual devices components are reduced. Accordingly, even the two masking step approach described in the Bobeck et al article has serious disadvantages.
Accordingly, it is a primary object of the present invention to provide a fabrication process for formation of magnetic bubble domain devices using only a single masking step.
It is another object of this invention to provide a fabrication process for making magnetic bubble domain devices using only a masking step, which can be used to provide devices having multiple metallic layers where these layers can be interchanged in their order of deposition.
It is a still further object of this invention to provide an improved fabrication process for making magnetic bubble domain devices which can be used with a plurality of materials and for provision of devices having any number of layers.